1. Field of the Invention
This invention relates generally to power chain saws and, more particularly, to safety devices as may be applied to alerting persons in the vicinity of a chain saw that they are in a zone of danger for potential injury from flying chain fragments in the event of a break in a cutting chain. More specifically, the present invention pertains to a chain saw hazard warning light, and a method for using the same, to warn personnel away from a zone of danger during operation of the chain saw portion of a forest harvester.
2. Background Art
Power chain saw operators and nearby personnel have incurred bodily injury and even death when hit by flying fragments of a broken cutting chain. This phenomenon, sometimes referred to as “chain shot,” can happen both on a manual chain saw as well as on a forest harvester equipped with a chain saw. Causes for breakage include improper chain tension, maintenance or repair, a damaged chain drive sprocket, chain guide bar and/or cutting chain, improper chain guide bar and chain lubrication, or excessive chain speed. Since a cutting chain can travel as much as 15,000 revolutions per minute around a chain guide bar, broken chain fragments will virtually always fly off at high velocity close to or within a plane that includes the chain guide bar. The direction of movement of chain fragments can be either in the direction that the chain guide bar is pointing at the time of chain breakage or in the opposite direction. In the case of a forest harvester, there is a direct hazard to the operator in the harvester cab when the chain guide bar is pointing toward the cab because chain shot has been known to penetrate the cab window under those circumstances and strike the operator within the cab.
One approach to reducing the hazard presented by a broken cutting chain has been to impose restrictions on the movement of broken chain ends and chain fragments. For a hand-held chain saw, U.S. Pat. No. 7,690,407 B2 issued to Annala disclosed a protective wall positioned in the vicinity of the chain drive gear that was capable of receiving the movement of the tail of the broken cutting chain and guiding the broken chain in a desired direction. U.S. Pat. No. 5,101,567 issued to Cool disclosed a safety switch that deenergized the chain drive of a hand-held chain saw in the event of a break in the cutting chain, and also disclosed a chain braking mechanism and safety guard to effect stoppage of the cutting chain motion. U.S. Pat. No. 4,805,308 issued to Ritola disclosed a roller attachment to the handle of a hand-held chain saw. The roller was aligned with the chain guide bar so as to extend substantially perpendicularly through the plane defined by the chain guide bar in order to intercept the saw chain should it become derailed. U.S. Pat. No. 4,315,370 issued to Horne disclosed a finger piece that acted as a safety surface in the event of breakage of the cutting chain on a hand-held chain saw. The finger piece was located far enough forward from the chain drive to force the whipping length of the chain to pivot and catch the broken chain.
The present invention, however, takes a different approach to the chain shot problem—namely, provision of a hazard warning light, preferably a flashing strobe light, illuminating just the chain shot danger zone to warn personnel away from that zone during operation of a chain saw. In other contexts, flashing lights and focused warning sounds have been used to warn of safety hazards. U.S. Pat. No. 6,587,043 B1 issued to Kramer disclosed a driver warning system that detected vehicle handling conditions and produced warnings in the form of arrays of flashing lights and/or a warning buzzer directed to the vehicle driver only, the intensity of which warnings was correlated to the seriousness of the safety hazards detected by the system. Patent Application No. US 2007/0102591 A1 of Toth disclosed a warning system for intersections, particularly railway crossings, that could identify when a train or vehicle was approaching an intersection and emit a sound warning beam that was focused into a danger zone. The approach taken by Kramer, i.e., by analogous reasoning, directing a hazard warning to the operator of a chain saw only, would be inadequate because nearby personnel who may be endangered by chain shot would not receive the warning. The approach taken by Toth, i.e., by analogous reasoning, focusing and projecting a sound warning into a chain shot zone of danger, would also be inadequate because the loud noise generated by the chain saw itself would tend to drown out the sound warning such that nearby personnel would likely not hear it.